In case of mobile communication systems, if a building is constructed on the periphery of a radio base station and if the installation situation of the base stations on the periphery of the radio base station changes, then the radio environment related to this radio base station changes. Therefore, conventionally, an operator performs a drive test of measuring a radio environment using a measurement vehicle provided with a measurement equipment, and collecting a measurement result and location information.
Such measurement and collection, for example, may contribute to the optimization of the coverage of a radio base station, but face the problem of too many man-hours and high cost. In this regard, according to 3GPP (3rd Generation Partnership Project) which is a project aiming to standardize a mobile communication system, a radio terminal owned by a user is used to proceed with the specification design of MDT (Minimization of Drive Test) for automation of the measurement and collection (refer to Non Patent Literatures 1 and 2).
As a type of the MDT, there is a log-type MDT (hereinafter, appropriately Logged MDT). According to the Logged MDT, a radio terminal in an idle state (that is, a standby state) performs radio environment measurement according to a preset measurement parameter, logs a measurement result as MDT data together with location information and time information, and holds the MDT data in order to report the MDT data to a network later. Using the MDT, the operator is able to recognize a location (so-called a coverage hole) with low received power or received quality from a radio base station.